Charm photoproduction at 20 GeV including preliminary lifetime results with improved optical resolution

Sixty five charm events have been observed in an exposure, during 1983, of the SLAC Hybrid Facility (SHF) to a backward scattered laser beam. Preliminary results for the charmed meson lifetimes have been obtained based on 19 neutral and 22 charged decays thereby doubling our earlier data. These lifetimes are consistent with our published results and the two data samples have been combined. From the resulting 42 neutral, 45 charged and 13 topologically ambiguous decays the charmed meson lifetimes are measured to be tau/sub D/sup 0// = (6.4/sub -0.9//sup +1.1/ +- 0.5) x 10/sup -13/s and tau/sub D/sup + -// = (8.2/sub -1.1//sup +1.3/ +- 0.6) x 10/sup -13/s and their ratio tau/sub D//sup + -///tau/sub D/sup 0// = 1.3/sub -0.3/sup +0.5/. The inclusive charm cross-section at a photon energy of 20 GeV has been measured to be 60 +- 8 +- 21) nb.